Chapter 9: Gravity (from Lecture Slide) Flashcards

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1
Q

Newton discovered that gravity is

A

Universal

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2
Q

Newton hypothesized that the moon is

A

Constantly falling towards Earth

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3
Q

Compared motion of the moon to that of a cannonball being

A

Fired from the top of a high mountain

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4
Q

If fired fast enough, the cannonball would

A

Fall around the Earth (satellite)

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5
Q

Aristotle’s time:

A

Motion of planets and stars is natural

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6
Q

Aristotle’s time not governed by

A

The same laws as objects on Earth

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7
Q

Newton is recognized that

A

A force directed toward the Sun because it must act on planets and other celestial bodies

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8
Q

Newtonian synthesis

A

The same set of laws apply to both celestial and terrestrial objects

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9
Q

Law of Universal Gravitation

A

Everything pulls on everything else

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10
Q

Every body attracts every other body with a force that is

A

Directly proportional to the product of their masses and inversely proportional to the square of the distance separating them

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11
Q

The Universal Law of Gravity: Proportionality relationship

A

1) Constant r
2) Constant m1 and m2

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12
Q

1) Constant r

A

The greater the masses m1 and m2 of two bodies, the greater the force of attraction between them

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13
Q

2) Constant m1 and m2

A

The greater the distance of separation r, the weaker the force of attraction

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14
Q

Gravitational force is

A

The weakest of the 4 fundamental forces

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15
Q

Four fundamental forces are included:

A

1) Gravitational force
2) Weak force
3) Electromagnetic force
4) Strong force

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16
Q

The gravitational constant G, which links force with mass and distance, is universal because

A

It is the same everywhere in the universe, and this universality feature pi (r)

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17
Q

The gravitational force between you and the Earth is much

A

Greater

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18
Q

The weight at the Earth’s surface is

A

The same as the gravitational force between you and the Earth at Earth’s surface

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19
Q

Acceleration due to gravity, g

A

1) Directly proportional to the mass of the Earth
2) Inversely proportional to the square of the distance from the center of the Earth

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20
Q

Inverse square law: gravity and distance

A

1) Intensity of an effect is inversely proportional to the distance from the source
2) Newton law of gravitation, electrostatic, light, sound and radiation phenomena follow an inverse square law

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21
Q

For increase in distance, there are decreases in

A

Force (intensity)

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22
Q

At great distance, force approaches but never reaches

A

Zero

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23
Q

The force of gravity between two planets depends on their

A

Masses and separation distance

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24
Q

Weight

A

Force an object exert, against a supporting surface

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25
Q

Standing on a scale in an elevator accelerating downward, less compression in scale springs, Weight is:

A

Less

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26
Q

Standing on a scale in an elevator accelerating upward, more compression in scale springs, Weight is:

A

Greater

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27
Q

At constant speed in an elevator, no change in

A

Weight

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28
Q

When you stand still on a bathroom scale that is supported on a stationary floor, this tells that

A

Your weight is at rest

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29
Q

Gravitational force between you and Earth pulls you

A

Against the supporting floor and the scale

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30
Q

Newton 3rd laws: the floor and scale push upward on you. Repeat this weighing procedure in a moving elevator, your weight reading varies

A

Not during steady motion but during accelerated motion

31
Q

Weightlessness:

A

No support force as in free fall

32
Q

Astronauts are without a support force and are continuously feeling

A

Weightless

33
Q

Elevator is at rest or moving at constant speed, the weight is

A

The same

34
Q

Elevator accelerates upward, floor and scale push

A

Harder against your feet, so the weight is feel “greater”

35
Q

Elevator accelerates downward, floor and scale push

A

Less against your feet weigh feels less

36
Q

Elevator in free fall and support force and scale reading are

A

Zero, and you are weightless

37
Q

There is still a gravitational force (mg) and still accelerates downward (g) but gravity is now

A

Not feel as weight because there is no support force

38
Q

The difference between ocean levels at different times of the day are called, what?

A

Tides

39
Q

There are typically two high tides and two low tides are what day?

A

Each day

40
Q

Ocean tides are caused by

A

The gravitational attraction of the Moon and the Sun

41
Q

Unequal tugs on Earth’s ocean causes what?

A

A stretching effect that produces a pair of ocean bulges

42
Q

Because the two bulges are on

A

Opposite sides, and high tides occur approximately every 12 hours

43
Q

The sun also contributes to ocean tide, but is

A

Less effective

44
Q

During the new Moon, or full Moon, the effects of Moon and Sun were

A

Add up, causing more pronounced spring tides

45
Q

When the Moon is halfway between a new and full Moon, the tides due to Sun and Moon partly

A

Cancel each other that causing less pronounced neap tides

46
Q

Earth and Moon are pull on what?

A

Each other

47
Q

How do the Earth and the Moon interact without touching?

A

The interaction between Earth and Moon is action at a distance

48
Q

One way to know that Earth is surrounded by

A

A gravitational field

49
Q

Moon interacts with the same as Earth, what?

A

A gravitational field also

50
Q

Gravitational fields are represented by

A

Field lines radiating into the object (Earth)

51
Q

Gravitational field (inward direction)

A

Indicating that the force is always attractive to Earth

52
Q

The crowding of arrows closer to Earth indicates that

A

The magnitude of the force is larger closer to Earth

53
Q

Gravitational field (symbolized)

A

Field strength decreases with increasing radii (gr = 1/r^2)

54
Q

Gravitational field inside the planet, g strength decreases to

A

Zero at the center

55
Q

The force due to the upper half of the Earth cancels the force due to

A

The lower half at the center of the Earth

56
Q

Similarity, any force due to any position of the Earth at its center will be cancelled by

A

The portion opposite to it

57
Q

Outside a planet, it is

A

Decreases to zero at “infinity” because you are farther away from planet

58
Q

Suppose you dig a hole through Earth to the other side and jump in, as you fall, your acceleration toward the center will

A

Go on decreasing

59
Q

At the center, your acceleration will be zero but your speed is

A

Maximum

60
Q

past the center you will be pulled back up, but because

A

You have acquired sufficient speed you will get to the other side

61
Q

Einstein’s theory of gravitation: Gravitational speed is

A

A warping of space-time by any mass and the warped space time affect the motion of other objects

62
Q

Light emitted by distant object pass by

A

More massive object in the universe

63
Q

The gravitational built from these objects can

A

Distort or bent the light

64
Q

Strong gravitational lensing results in

A

Multiple images of these objects

65
Q

Weak gravitational lensing result in

A

Objects appearing distorted, stretched, or magnified

66
Q

When a start exhausts nuclear fuel, it shrinks, so that its mass becomes

A

Concentrated within a smaller radius

67
Q

Gravitational force on the surface increases because when

A

D decreases and F increases

68
Q

Black hole: When a collapsing star becomes so small that

A

Its gravitational field exceed the threshold for allowing anything, even light, to escape, a black form is formed, trapping everything inside forever by warped spacetime

69
Q

Wormhole (definition)

A

A distortion of space-time

70
Q

Instead of collapsing toward an infinitely dense point, a wormhole opens out again in

A

Another part of the universe or in a different universe

71
Q

Universal gravitation

A

Everything attracts everything else

72
Q

Earth is round because of gravitation—all parts of Earth have been

A

Pulled in, making the surface equidistant from the center

73
Q

The universe is expanding and accelerating outward, pushed by mysterious

A

Dark energy

74
Q

Galaxies exhibit extra gravitational pull attributed to mysterious

A

Dark matter